1. Field of the Invention
The invention relates in general to a generator, and more particularly to a displacement type generator which converts a unidirectional magnetic flux into a multi-polar magnetic flux.
2. Description of the Related Art
Conventional electromagnetic generators use the magnetic flux change generated by the relative movement between the coil and magnetic field, and then output a voltage generated in the coil according to Faraday's law. The electromagnetic generators can be divided into rotary type and displacement type generators according to the type of relative movement. The conventional rotary type generator, having the advantages of high conversion efficiency and large volume of power generation, has been widely used in large-scale generator facilities. However, the rotary type generator is disadvantaged by its big size.
In Japan Patent No. JP2001327197, people's acting force applied to the floor is converted into a rotation force, which is then used in the generator integrated with the walking auxiliary tool such as shoes or stick. In British Patent No. GB2359593, the displacement generated by the weight of a vehicle moving on the road is transmitted by a mechanical or fluid links to provide input to a rotary machine which powers an electrical power generator. In U.S. Pat. No. 4,434,374, the energy of a pedestrian or a vehicle is captured and converted into an input torque of a rotary type generator via a linking and transmission device. In British Patent No. GB2065983, a conversion mechanism is used for converting a reciprocating movement into a rotation movement, which is connected to a rotary type generator. In 1998, Massachusetts Institute of Technology disclosed a rotary type generator, which is disposed in sneakers and is driven by the acting force of the heel during walking. In 2005, the University of Pittsburgh also disclosed a suspended-load backpack, which converts mechanical energy from the vertical movement of carried loads to electricity via a rotary type generator with a toothed rack attached to the load. The rotary type generator has higher efficiency in electromagnetic conversion but normally needs to be combined with a mechanism such as spring, flywheel, and reduction gear. Therefore, the rotary type generator is complicated in structure, the integration with other components or devices is difficult, the magnitude of movement is large, and the reliability is hard to be increased.
The displacement type generator has a simpler structure and higher reliability compared with the rotary type generator. In Japan Patent JP2007215345, a plurality of magnets are arranged with their center axes aligned so that the adjacent magnetized poles repel each other to form a magnet bar, and a winding coil is fixed in the grounding at a position facing the boundary of these magnets. The power is generated by utilizing the movement of the magnet bar caused when persons walk or vehicles pass thereupon. United States Patent No. US2008084121, US2008054731, US2005225181, US2005231044, US2008036306 and World Patent No. WO9831090 each disclosed a linear generator that is constituted by magnets and coils, and the relative reciprocating movement between the magnets and the coils enables the coils to generate induction power. In 2004, Dr. Duffy of NUI Galway (National University of Ireland) disclosed a design of electromagnetic generators that can be integrated within shoe soles, when the pedestrian walks and the magnet wobbles, the device is driven to generate power. Generally speaking, the displacement type generator generates reciprocating movement by moving the magnet inside the coil. The moving stroke of the magnet is usually not small, and the magnetic flux loop is an open circuit, so the displacement type generator has the disadvantages that both the magnetic flux of the magnet and the utilization of magnetic energy are not high, the magnetic field leaks and is easily interfered, such that the efficiency is poor and power generation is small.
The induced voltage is determined by the number of coils and the change of the magnetic flux. In order to increase the efficiency in power generation, the relative speed between the magnet and the coil has to be increased so as to increase the magnetic flux rate. Using a multi-polar magnet can increase the switching frequency of the magnetic flux, however, the multi-polar magnet suffers from low magnetic working point with the constraint of shape and size.